Reporter: Thanksgiving morning 2012. Interstate 10, west of beaumont, texas. The highway crowded with holiday travelers. Happy thanksgiving, everyone. We're looking at fog in the morning. Reporter: On one of the busiest travel days of the year, fog and speed, the limit recently raised to 75, form a perfect storm for a highway catastrophe. You will never forget this thanksgiving. No, no, no. Not anytime soon. Reporter: Catie and matt stegmoyer heading for ohio with their children. They drive from sunshine into a wall of fog. I mean, fog like I had never seen it. It was so thick that it was actually, I had to use the wiper blades, because it was condensing on the windshield. Reporter: Police dashcam video of i-10 that very morning. In an instant, daylight to danger. Through the fog, catie stegmoyer spots a truck dead ahead. She stops just in time, but all around, other drivers fly blissfully right on by. I kept telling matt, they don't know, they don't know, they don't know to stop and then they started piling up on each other. Reporter: Ahead, a mazda has rear-ended a chevy tahoe. It's a simple fender bender. But it sets off one of the biggest chain reaction crashes in history. A massive crash. Mangled metal as far as the eye can see. Bam, you could hear it for miles. Reporter: Somebody described it as a demolition derby. I think that would probably be a fair assessment at that point in time, yes. Reporter: A sense of the bedlam in texas from other crashes caught on camera in another place and time. Imagine that, multiplied by 100. Back in texas on thanksgiving morning, the full-contact traffic jam continues. There's a major accident! On i-10, I mean, there's tons of trucks and cars. Big rigs hitting big rigs and hitting little cars. Oh, my god, oh, my god. Reporter: Police and cell phone video reveal an instant junk yard. But only from the air does the scope of the destruction become clear. More than a mile of mayhem. 24 separate crashes involving 118 vehicles. Look at this. Kids on the side of the road. Oh, my god. Reporter: Stunned travelers emerge from cars. They wander through still dense fog in the highway median. In this part of texas, everything depends on local first responders. The nearest is the hamshire volunteer fire department. Nick morrison, an oil field commander. Cars are still coming. And the fog isn't lifting. And, just how much bigger is this going to get? Reporter: When is it going to stop? You couldn't see, so you didn't know where the cars were going, where they were wrecking, or if they were going to come and hit you. Reporter: Down the highway, the stegmoyers are still in the eye of the storm, they just don't know it. Catie, a nurse, wants to help. So, your nurse's instincts kicked in? Yes. I liked to think my motherly instincts kicked in first, and i said, you guys are okay here, I'm going to check on other people. Reporter: But the wreck isn't over. In the fog, where his wife just disappeared, matt hears another collision. There was a giant semi on top of a car where my wife was. Reporter: Eventually, catie calls. Shaken by a close call, but unharmed. When I finally got ahold of him, he just held me, and he's like, I thought you were dead, and I said, I almost was. Reporter: But the pileup isn't finished with them. A white suv plows into a car behind theirs. Matt stegmoyer knows, usually in an accident, it is safest to stay in your car. But there is nothing usual about this accident. You knew you had to get out. Yeah, it was just, it was just a bad feeling. Reporter: Matt has a wrenching choice -- conventional wisdom says, stay in the car. But survival instinct says, go. In a flash of father's intuition, he decides. And so, I grabbed both kids and ran. Reporter: And not a moment too soon. A semismashes into the pile, crunching their car, which is now, fortunately, empty. The back of the semiwas right where brandon's head was. And I looked at it and I just - I said, my kids were in that car. Reporter: But the couple in that white suv just behind the stegmoyers did not and could not run away. When that truck hit, they were killed. The only fatalities in the entire wreck. And it happened just inches from where the stegmoyer children had been. You could hear cars hitting in the fog and you could see he headlights going back and forth as people were swerving. Reporter: Drive david perryman helped carry stretchers and comfort the injured. He remembers one particular young man. I was trying to take his mind off of what was happening. I said, what do you like about thanksgiving dinner, what is your favorite part of it? And he almost smiled and he whispered, "all of it." Reporter: Chain reaction multivehicle crashes are usually caused by snow or fog. Which was the cause of this 95-vehicle crash in virginia on easter sunday. They happen more often than you may think. There were 44 deadly pileups of ten or more vehicles between 2007 and 2011. And the stegmoyer's, well, they reached ohio, where their long-delayed thanksgiving was sweet. You had a lot to be thankful for. Oh, gosh yes. We pulled into his parents' driveway and his mom, in the driveway, she just, tears coming, I'm crying, she's like, give me my babies, you know? And it came so close. It came so close.

This transcript has been automatically generated and may not be 100% accurate.

Now Playing: Gretchen Carlson on Dealing with Sexual Harassment at Work: Part 3

Now Playing: {{itm.title}}

{"id":19054673,"title":"Pile-Up: 118 Vehicles","duration":"6:08","description":"Meet a couple who survived one of the worst multiple vehicle accidents in U.S. history.","url":"/2020/video/pile-118-vehicles-19054673","section":"2020","mediaType":"default"}